Circadian Modulation of Ventricular Tachycardia Cycle Length Variability in ICD Patients with Dilated Cardiomyopathy

VT is usually characterized by stability of the RR intervals after a few cycles from the onset. The aim of this study was to evaluate the VT cycle length (VTCL) variability in patients with dilated cardiomyopathy (DCM), in whom a third-generation ICD was previously implanted. Eighty-three episodes of VT were analyzed in 10 patients (8 male, 2 female, 65 ± 6 years) with DCM, and NYHA Class II (7 patients) or III (3 patients). As an index of VTCL variability, the coefficient of variance of the last 15 consecutive RR intervals (CVRR) of the detected and stored VT by the device was considered. The mean value of the RR intervals and the mean value of CVRR of the VT episodes recorded during day versus night time were compared. Fifty-five VT episodes were recorded during the day and 28 episodes during the night time. The mean RR intervals of VT episodes during day time was 335 ± 29 ms and during the night time was 350 ± 22 ms (P = NS). The mean CVRR of VT episodes during day time and night time were 2.83 ± 0.52 and 3.36 ± 0.48, respectively (P = 0.017). In conclusion, a circadian modulation of VTCL variability exists in patients with DCM. The VTCL variability is less during day time compared to night time. A possible explanation is a circadian alteration of sympathovagal balance modifying the electrophysiological properties of the arrhythmogenic substrate.